The present invention relates to ultrasonic surgical equipment and, in particular, to ultrasonic surgical handpieces, resonating bars or horns and related ultrasonic cutting tips. Ultrasonic surgical handpieces, resonating bars or horns and related ultrasonic cutting tips are the critical and principal parts of ultrasonic surgical equipment.
A typical ultrasonic surgical device consists of an ultrasonically driven handpiece with attached cutting tip and irrigating sleeve and an electronic control console. The handpiece assembly or probe is attached to the control console by an electric cable and flexible tubings. Through the electric cable, the console varies the power level transmitted by the handpiece to the attached cutting tip and the flexible tubings supply irrigation fluid to and draw aspiration fluid from the eye through the handpiece assembly.
The operative part of the handpiece is a centrally located, hollow resonating bar or horn directly attached to a set of piezo-electric crystals. The crystals supply the required ultrasonic vibrations needed to drive both the horn and the attached cutting tip during surgery and are controlled by the console. The crystal/horn assembly is suspended within the hollow body or shell of the handpiece by flexible mountings. The handpiece body terminates in a reduced-diameter portion or nosecone at the body's distal end. The nosecone is externally threaded to accept the irrigation sleeve. The horn has a bore that is internally threaded at its distal end to receive the cutting tip. The irrigation sleeve also has an internally threaded bore that is screwed onto the external thread of the nosecone. The cutting tip and sleeve are sized so that the tip projects only a predetermined amount past the open end of the irrigating sleeve. Ultrasonic surgical instruments, cutting tips and irrigating sleeves are more fully described in U.S. Pat. Nos. 3,589,363, 3,693,613, 4,180,074, 4,223,676, 4,515,583, 4,573,979, 4,578,059, 4,609,368, 4,634,420, 4,643,717, 4,652,255, 4,681,561, 4,705,500, 4,787,889, 4,808,154, 4,816,017, 4,816,018, 4,869,715, 4,922,902 and 4,983,160, the entire contents of which are incorporated herein by reference.
In use, the ends of the cutting tip and irrigating sleeve are inserted into a small incision of predetermined size in the cornea, or other surgical site. The cutting tip is ultrasonically vibrated within the irrigating sleeve by the crystal-driven ultrasonic horn, thereby emulsifying the selected tissue in situ. The hollow bore of the cutting tip communicates with the bore in the horn that in turn communicates with the aspiration line from the handpiece to the console. A reduced pressure or vacuum source in the console draws or aspirates the emulsified tissue from the surgical site through the open end of the cutting tip, the cutting tip and horn bores, and the aspiration line into a collection device on the console. The aspiration of emulsified tissue is aided by a saline flushing solution or irrigant that is injected into the surgical site through the small annular gap between the inside surface of the irrigating sleeve and the cutting tip and by ports at the distal end of the sleeve.
As discussed in U.S. Pat. Nos. 4,681,561 and 4,816,017 to Hood, et al., one desirable characteristic of ultrasonic handpieces is consistent, linear power delivery to the cutting tip over the entire power band. Power surges and drop offs are undesirable, particularly during microsurgery in the eye. Most prior art surgical handpieces exhibit linear power delivery over the upper two-thirds of their power band. However, in the lower portion of the power band, many prior art handpieces do not exhibit linear power delivery. As a result, as the surgeon slowly increases the power to the piezo-electric crystal in the handpiece at the lower end of the power band from an off position, few if any of the crystal vibrations are transmitted longitudinally down the cutting tip shaft to the distal end of the cutting tip until some minimum power level is reached, at which point the distal end of the cutting tip suddenly begins to vibrate. Correspondingly, as the power to the piezo-electric crystal is slowly reduced from above to below this minimal point, the ultrasonic vibrations at the distal end of the cutting tip abruptly stop. As a consequence, control of the handpiece at the lower portion of the power band below this minimal power level is lost, thereby decreasing the usable power band of the handpiece and introducing power surges and drop offs.
This phenomenon never has been explained fully in the prior art. For example, in their U.S. Pat. Nos. 4,681,561 and 4,816,017, Hood, et al. disclose that the presence of cavitation bubbles has an effect on the stability of the surgical handpiece by creating variations in the mechanical impedance in the handpiece that cause corresponding variations in the mechanical operating characteristics of the handpiece. The decoupling sleeve disclosed in these patents serves to reduce these variation by isolating the handpiece shell from the cutting tip. While this decoupling sleeve is extremely efficient at reducing cavitation bubbles and minimizes power surges and drop offs, the sleeve must be manually installed on the handpiece and discarded after each use, adding extra work and expense to the surgical procedure. Accordingly, a need continues to exist for an ultrasonic handpiece that has inherent linear power delivery and does not require the use of external stabilizing devices.